"There are serious and persistent problems with ticket sales throughout the airline industry as a whole. It is completely unacceptable," Kuneva said in a statement.
The seven operators, some already criticized for Web sites run in other European nations, were accused by Denmark´s consumer ombudsman of misleading consumers on booking procedures, notably on prices and terms under which flight tickets can be used.

Henrik Oee said his investigation involved 13 foreign companies that run online travel services in Denmark, five of which have already moved to change their practices.
The seven others were still in violation, he said in a statement from Copenhagen.

"Consumers have the right to know where to keep a close watch," he said.

Kuneva´s spokeswoman Helen Kearns said online booking agency Seat24 pledged to bring its Web site inline with EU rules by August, but that Irish low-cost carrier Ryanair and German low-cost airline Air Berlin had disagreed with the Danish conclusions.

Kuneva said in May that a third of people who shop for flights online in the EU were being cheated by misleading ads and prices. She gave airlines and travel operators one year to fall in line with EU consumer rules or face legal action.

The EU investigation so far has indicated that the main problems are misleading pricing and vague conditions and contract terms. Airlines and other travel companies often add airport taxes, handling fees, baggage and seating charges and other costs on top of the prices that first appear on Web sites.